Aspects of the present invention pertain to a cooling system and a method for cooling electronic devices such as a hard drive, an optical device, a battery, a central processing unit (CPU) or other integrated circuit device of a computer and more particularly, of a laptop/notebook computer.
Advances continue to be made in the manufacture of solid-state electronic devices, resulting in increasing functionality, density, and performance of the integrated circuits (ICs). The amount of heat generated, and accordingly the amount of power needed to be dissipated, by modern integrated circuits generally increases with increases in the density and speed of the circuits. Removal of heat produced by the integrated circuits therefore continues to be of a significant concern in modern integrated circuit package and system designers. For instance, a loss of performance and the degradation in reliability of integrated circuits may occur and often does when the circuits operate at elevated temperatures.
In addition, the trend toward more compact electronic systems is also continuing, thus exacerbating the thermal problem produced by the high-complexity and high-performance integrated circuits. For example, laptop or notebook sized computers have recently become quite popular, with continuing market pressure toward even smaller computer systems such as personal digital assistants (PDA). However, these small computer systems eliminate many of the traditional techniques for heat removal available for large-scale computer systems, such as the use of fans for convection cooling of the integrated circuits.
Many methods and apparatuses have been developed to remove heat from heat generating components located within the confines of a computer system enclosure. Many methods employ a fluid flow model to dissipate heat generated from the components such as immersing the components in a pool of inert dielectric liquid, using thermosyphons where a liquid evaporates with applied heat and condenses dissipating that heat elsewhere in a closed system, and using heat pipes where the liquid evaporates, condenses at another region and reaches the hot area through wick structures that line the heat pipes.
FIG. 1 illustrates a direct liquid cooling system. An electronic device that generates heat such as a central processing unit (CPU) 102 is cooled by a direct liquid cooling device 100. The CPU 102 is coupled to a substrate 104 which is typically placed on a printed circuit board (PCB) 104. Methods to attach the CPU 102 to the substrate 104 and to the PCB 106 are well known in the art. A manifold 108 is placed over the CPU 102. The manifold 108 includes a liquid inlet 110 and liquid outlets 112A and 112B. Gaskets 114 may be included to attach or place the manifold 108 over the CPU 102. The gaskets 114 also function to seal the manifold 108 over the CPU 102 to prevent liquid from leaking out of the device 100. In the cooling device 100, liquid is injected and dispensed or flown over the CPU 102 via the inlet 110. Liquid is flown out of the manifold 108 via the outlets 112A and 112B taking the heat transferred from the CPU 102 to outside of the system. The liquid is typically recycled back into the cooling device 100 via a pump action.
FIG. 2 illustrates another cooling device 200 which is similar to the device 100 with the addition of a plate 116 having a plurality of orifices 118 to increase the surface area that the liquid can contact the CPU 102. The plate 116 can be placed below the liquid inlet 110. Liquid passing through the inlet 110 is distributed over the plate 116 and dispensed over the CPU 102 via the orifices 118. The liquid thus can contact a wider area of the CPU 102 more uniformly. A pump is typically used to cause the liquid to jet through the orifices 118, hence, the cooling device 200 is often termed a jet impingement cooling device.
FIG. 3 illustrates an example of a cooling device 300. The device 300 employs a cross flow configuration to flow liquid across an electronic device. As shown in FIG. 3, an electronic device (e.g., a CPU 102) is placed on a substrate 104 which is typically placed on a PCB 106. A manifold 120 is placed over the CPU 102 using gaskets 114 to couple and seal the manifold 120 over the CPU 102. A liquid inlet 122 and a liquid outlet 124 are included in the manifold 120. Liquid is flown across the CPU 102 and out of the outlet 124. The liquid travel path can be configured to be recycled so that the liquid is recycled for the cooling device 300.
The cooling devices described have several disadvantages. Devices similar to the cooling devices 100 and 200 tend to be too large and thus not practical for small electronic devices where spaces are limited and electronic devices need to be cooled are typically placed in small confines of a slim/small design (e.g., laptop or notebook computer). Devices similar to the cooling devices 100 and 200 use a jetting device to accelerate the liquid over the CPU 102 and that may exert too much pressure on the CPU 102. Devices similar to the device 300, on the other hand, can be small but do not have the liquid flowing fast enough to increase efficiency of the cooling devices. Additionally, the liquid tends to stay stagnant above the CPU thus heat generated by the CPU is not transferred or removed quick enough